1. Related Application
U.S. patent application of L. Young entitled "Differentially Pumped Seal Apparatus" Ser. No. 062,038 filed 06/15/87.
2. Field of Invention
This invention relates to an improvement in systems having a differentially pumped seal apparatus such as in a particle beam lithography system.
3. Prior Art
U.S. Pat. No. 4,524,261 of Petric et al entitled "Localized Vacuum Processing Apparatus" (hereinafter called the '261 patent) and U.S. Pat. No. 4,528,451 of Petric et al entitled "Gap Control System for Localized Vacuum Processing" (hereinafter called the '451 patent).
The use and advantages of a localized vacuum processing apparatus (hereinafter called a seal apparatus) in a particle beam lithography system for treating a workpiece (substrate), such as a semiconductor wafer or mask, by a particle beam are disclosed in the '261 patent and the need for controlling of the gap length (size) between the tip of the seal apparatus and the workpiece are disclosed in the '451 patent.
The seal apparatus of the '261 patent comprises a housing member with centrally located sleeves forming concentric apertures connected to vacuum pumps to create zones of radially inwardly increasing vacuum with the center most aperture being at highest vacuum. In this manner, only the area of the workpiece proximate the sleeves is subjected to vacuum while the rest of the workpiece surface is at ambient pressure. The gap between the tips of the sleeves and the workpiece surface is important, and the '451 patent discloses a sensing and feedback control system for continuously monitoring and changing the gap length so as to be within a selected range by moving the workpiece up and down during workpiece processing. In the '261 patent, as well as in the '451 patent, the workpiece is moved transversely of the seal apparatus to treat the workpiece in an otherwise conventional manner.
The seal apparatus of the '261 patent was improved by the differentially pumped seal apparatus disclosed and claimed in the Young application, supra, by providing higher conductance and better pump efficiencies and operating with a much smaller gap between the workpiece and the seal apparatus. Otherwise, the operation of both apparatus is similar in a particle beam lithography system. That is to say, the workpiece is subjected to vacuum proximate the concentric sleeves and the remainder of the workpiece is at ambient pressure and the workpiece is moved transversely of the sleeves during workpiece processing.
In either case, since the area of the workpiece surface beneath the concentric sleeves is at low pressure and the innermost aperture is open to the beam column, while the remainder of the workpiece surface is at ambient pressure, there is a possibility of contaminants coming in contact with the workpiece surface and entering the beam column and this invention is directed toward reducing this possibility.